ES2545273T3 - Electrical system and control procedure - Google Patents

Abstract

A power generation system (10) comprising: at least two electrical systems (18) connected by means of a medium voltage capture system (80) with an electrical connection point (16), said electrical connection point being (16) a common connection point with a network (14), each electrical system (18) comprising a power conversion system (20) comprising a respective DC to AC converter (32) including a plurality of switches ( 34) to convert a direct current power into an alternating current power; and a control system (24, 25) including at least two pulse width modulation modulators (36), each pulse width modulator (36) obtaining a fundamental waveform to generate a pulse width pattern and to provide the pulse width pattern to a respective DC to AC converter (32) to actuate the switches of the respective DC to AC converter (32); wherein the control system (24, 25) is configured to interleave the fundamental waveforms of the at least two electrical systems to generate interleaved pulse width patterns respectively for the at least two DC to AC converters (32 ), wherein each power conversion system (20) further comprises a respective generator side converter (30) for converting an alternating current power from a wind turbine generator (28) into a direct current power ; and in which the control system further comprises a master controller (25) connected to the electrical connection point (16), characterized in that: the pulse width modulators (36) additionally obtain a carrier signal and use the waveform fundamental waveform and carrier signal to generate a pulse width pattern, and the control system (24, 25) is further configured to interleave the fundamental waveforms and carrier signals or a combination of the fundamental waveforms and carrier signals .

Description

image 1

DESCRIPTION

Electrical system and control procedure

The invention generally relates to electrical systems for providing electrical power to public networks at interconnection points. More specifically, the invention relates to an electrical system that converts an electric power generated by renewable energy sources such as wind turbines and photovoltaic modules into an electric power that meets a low harmonic requirement of the interconnection point.

Recently, renewable energy sources, such as wind turbines, have received increased attention as alternative energy sources that are safe for the environment and relatively inexpensive. With this growing interest, considerable efforts have been made to develop wind turbines that are reliable and

10 efficient To maximize the efficiency of power generation and to simplify the connection to the public network, wind turbines are often located close to each other, which is generally referred to in relevant techniques such as "wind farm". The wind turbines in the wind farm generate an electric power and supply electric current to the public service, such as an electric grid, at a common connection point (PCC).

One type of wind turbine that maintains the speed of the rotational generator proportional to the wind speed is

15 a variable speed wind turbine. Examples of the variable speed wind turbine are described in, for example, US5083039 by Richardson et al. The variable speed wind turbine includes a generator, a converter on the generator side, a DC link busbar and a converter that is connected to the network. The variable frequency energy of the generator is transferred to the DC link busbar by the generator side converter and later becomes a fixed frequency by the converter

20 network side.

The active network side converter usually uses semiconductor switches, such as bipolar isolated gate transistors (IGBT), to convert DC voltage to AC voltage to the network frequency by means of pulse width modulated switching actions of those semiconductor switches. Switching actions tend to create undesirable harmonics. To avoid the problems caused by

25 these harmonics, a number of filters are installed. Filter components are usually bulky and expensive.

EP 1 995 863 discloses control procedures for synchronization and offset of the pulse width modulation strategy (PWM) of the power converters used to supply a high voltage network, in accordance with the preamble of claim 1.

There is a need in the art to provide an improved electrical system for a wind farm that can meet the requirement of low harmonics at an electrical connection point for a group of wind turbines that differs from conventional systems. Additionally, such systems would be useful for other renewable energy sources such as photovoltaic systems, for example.

Various aspects and embodiments of the present invention are thus provided, as defined in the appended claims.

Various features, aspects and advantages of the present invention will be better understood when the following detailed description is read with reference to the attached drawings, in which similar characters represent similar parts throughout the drawings, in which:

Figure 1 is a block diagram illustrating a wind farm according to an embodiment disclosed in this document.

Figure 2 is a block diagram of an electric wind turbine system according to an embodiment disclosed herein.

Figure 3 is a block diagram of a PWM modulator for generating PWM patterns for semiconductor switches of some converters in a wind turbine electrical system.

Figure 4 is a pair of graphs illustrating an exemplary fundamental waveform, a triangular carrier waveform, and a PWM pattern that is generated by comparing the fundamental waveform with the shape of triangular carrier wave.

Figure 5 is a set of graphs illustrating fundamental waveforms and triangular carrier waveforms for a corresponding phase of converters in different electrical systems of

50 wind turbine.

Figure 6 is a set of graphs illustrating PWM patterns for a corresponding phase of converters in different wind turbine electrical systems by means of a comparison of the fundamental waveforms and the triangular carrier waveforms of Figure 5.

image2

Figure 7 is a set of graphs illustrating fundamental waveforms and triangular carrier waveforms for a corresponding phase of converters in different wind turbine electrical systems according to another embodiment.

Figure 8 is a set of graphs illustrating PWM patterns for a corresponding phase of about 5 converters in different wind turbine electrical systems by means of a comparison of the fundamental waveforms and triangular carrier waveforms of Figure 7 .

Figure 9 is a set of graphs illustrating fundamental waveforms and triangular carrier waveforms for a corresponding phase of converters in different wind turbine electrical systems according to yet another embodiment.

10 Figure 10 is a vector diagram of harmonics vectors of four wind turbine electrical systems in accordance with one embodiment.

Fig. 11 is a vector diagram of harmonic vectors of four wind turbine electrical systems according to another embodiment.

Fig. 12 is a vector diagram of harmonic vectors of five wind turbine electrical systems according to another embodiment.

Fig. 13 is a block diagram illustrating a wind plant system that includes a substation system according to one embodiment.

Figure 14 is a block diagram of a photovoltaic electrical system in accordance with an embodiment disclosed herein.

20 Embodiments described hereinafter generally refer to a power generation system with at least two electrical systems that are connected in parallel at an electrical connection point such as an electrical network or a substation system of a power system. power generation For illustration purposes, the electrical systems are illustrated in Figures 1-13 as wind turbine electrical systems. Each wind turbine electrical system includes a pulse width modulation (PWM) controller to obtain a shape

25 of fundamental wave and a carrier signal, and to generate a PWM pattern for a respective network side converter to be used when switches of the respective network side converter are operated. A control system is configured to reduce harmonics at the electrical connection point by interleaving the carrier signals and fundamental waveforms, or a combination of carrier signals and fundamental waveforms to generate interleaved PWM patterns respectively for side converters

30 network of wind turbine electrical systems. Therefore, a combination of the waveforms of the wind turbine electrical systems at the electrical connection point has relatively low harmonics. Therefore, in one aspect, passive filter designs of wind turbine electrical systems can be significantly simplified. In another aspect, the switches of the network side converters are allowed to have a relatively low switching frequency, the energy losses of the

35 switches, and the power efficiencies of the network side converters are increased.

Figure 1 illustrates a wind farm 11 that includes a plurality of wind turbines 12 that are connected in parallel to supply electrical power to an electrical network 14 at an electrical connection point 16 which, in one embodiment, is a common connection point ( PCC).

An exemplary power generation system 10 for the wind farm 11 includes a plurality of

40 wind turbine electrical systems 18. Each wind turbine electrical system 18 includes a power conversion system 20 to convert an electric power that is generated by a generator 28 of the wind turbine 12 into an alternating current with a constant voltage and a constant frequency, and a turbine transformer 22 to transform the alternating current into a constant voltage and a certain frequency before the alternating current is supplied to the mains 14 in the PCC 16. The electrical system 10 includes a system of

A control that may comprise a plurality of turbine controllers 24, a master controller 25, or a combination of turbine controllers and master controllers.

Figure 2 illustrates an embodiment in which the wind turbine 12 includes a rotor 13 with blades 26 that are coupled with the generator 28 which in turn is coupled with the wind turbine electrical system 18. In one embodiment, the generator 28 It comprises a synchronous permanent magnet machine. The coupling of the rotor 50 with the generator 28 can be either a direct coupling or by means of an optional gearbox (not shown). The exemplary generator 28 is a synchronous generator, however, the invention can also be used with other generators such as double feed induction generators. In some embodiments, wind turbines 12 have generators with the same assigned output power, or a similar one. The turbine transformer 22 transforms the alternating current from a network side converter

55 32 on a lower voltage side 21 at a higher voltage on a high voltage side 23. In one embodiment, the wind turbine electrical system 18 further includes a passive filter 27 in series connection with the high voltage side 23 of transformer 22 for further harmonic reduction.

image3

The generator 28 is coupled by means of a stator (not shown) with the power conversion system 20 of the wind turbine electrical system 18. The power conversion system 20 receives electricity from the generator 28 and converts the electricity in a form suitable for delivery to the power grid 14 (Figure 1). The power conversion system 20 in the exemplary embodiment is an AC converter

5 CC-AC that includes a generator side converter 30, a DC link busbar 31, and a network side converter 32. Each of the generator side and network side converters 30 and 32 includes Switches 34. Switches 34 may comprise any suitable devices with several examples including bipolar isolated gate transistors (IGBT), gate communicated thyristors (GCT), and semiconductor oxide metal field effect transistors (MOSFET). In the embodiment illustrated, the generator side converter 30 and the network side converter 32 are two-level converters. In other embodiments, the generator side converter 30 and the network side converter 32 may be multi-level converters.

In certain embodiments, the network side converter 32 comprises a pulse width modulation converter (PWM) that includes three phases, each having two switches 34. In one embodiment, the controller

Turbine 15 24 includes a PWM modulator 36 that provides modulated PWM pattern signals 38 to control the switches 34. Therefore, the network side converter 32 transforms a direct current into the DC busbar 31 by means of the PWM pattern signals modulated 38 in a three-phase alternating current with a frequency and a controlled voltage.

In one embodiment, the PWM modulator 36 receives reference waveforms (current or voltage) at the PCC 16. In such embodiments, the reference waveforms for each wind turbine electrical system 18 are therefore identical and referred to as "global reference". In an alternative embodiment, as shown by dashed lines in Figure 2, the PWM modulator 36 receives reference waveforms from the output of the power conversion system 20, and reference is made respectively to the reference waveforms as "local references". Local references

25 of different wind turbine electrical systems 18 may be slightly displaced in terms of their phase. The phase quantities of the three phases Ua, Ub and Uc of an individual wind turbine electrical system 18 are separated from each other by 120 degrees.

Referring to Figure 3, the PWM modulator 36, in one embodiment, may comprise a phase tracking loop (PLL) circuit 40 for measuring a phase and an amplitude of a reference waveform, a reference generator 42 to receive the phase and amplitude information of the reference waveform and generate a fundamental waveform, and a carrier generator 44 to receive the phase information of the reference waveform and emit a carrier signal. A design of the PLL circuits for use with three-phase waveforms is described, for example, in US2007 / 0159265 of Weng et al.

In one embodiment, the carrier signal is a triangular waveform, and the PWM modulator 36 comprises

35 in addition a comparator 46 to compare the fundamental waveform with the triangular carrier waveform and generate a PWM pattern signal 38 to operate the switches 34 (Figure 2). In other embodiments, PWM modulators 36 are spatial vector PWM modulators, and each of the carrier signals is a switching signal with previously determined switching periods. In one embodiment, a ratio of the carrier signal frequency to the fundamental waveform frequency is an integer and can be used to generate synchronous PWM patterns. In other embodiments where the relationship is not an integer, the generated PWM patterns are asynchronous.

Referring to Figure 4, in one embodiment, the fundamental waveform comprises a sine waveform 50, the carrier signal comprises a triangular waveform 52, and a PWM pattern 54 is generated based on a comparison of the sine waveform 50 with triangular waveform 52. In one embodiment, when a

The instantaneous amplitude of the sine waveform 50 is greater than an instantaneous amplitude of the triangular waveform 52, the PWM pattern 54 is a logical (or active) "high" value. When an instantaneous amplitude of the sine waveform 50 is less than an instantaneous amplitude of the triangular waveform 52, the PWM pattern 54 is a logical (or inactive) "low" value. The pattern of PWM 54 thus formed is a series of pulses.

In a first embodiment of the invention, the PWM patterns for a corresponding phase, for example, the Ua phase, of different wind turbine electrical systems 18 are interleaved by means of the master controller 25 and / or each turbine electrical system controller wind 24 (figure 2). In a more specific example, the carrier signals for individual wind turbine electrical systems 18 have the same frequency and amplitude, but are interleaved in relation to each other throughout a cycle of carrier signals. For example, each carrier signal may be separated by a degree of 360 / n with respect to the carrier cycle from the

55 carrier signal of another wind turbine electrical system 18, where n is the number of wind turbine electrical systems 18 in the power generation system 10. For a power generation system 10 with four wind turbine electrical systems 18, in one embodiment, each carrier signal of one phase of the network side converter 32 is separated from each other by 90 degrees.

Referring to Figure 5, the carrier signals 152, 252, 352 and 452 of four turbine systems are displaced 90 degrees along the carrier cycle, and the fundamental waveforms 150, 250, 350 and 450 for four systems Electric wind turbine 18 are the same. In this example, a first, third and fourth carrier signals 252, 352 and 452 of the network side converters 32 of the second, third and fourth wind turbine electrical systems 18 are displaced respectively 90 degrees, 180 degrees, and 270 degrees with respect to a first carrier signal 152 throughout the carrier signal cycle.

image4

5 Figure 6 is a set of graphs illustrating the PWM patterns 154, 254, 354 and 454 for the embodiment of Figure 5. Each of the four PWM patterns 154, 254, 354 and 454 is a series of pulses with the same amplitude, and 90 degrees of the carrier signal cycle with respect to an adjacent PWM pattern are substantially interspersed.

In certain embodiments, for each wind turbine electrical system 18, the PWM modulator 36

The respective 10 includes three PLL circuits 40 with a PLL circuit for each of the three phases and is used to generate three PWM patterns for three phase switches. The PWM patterns actuate the switches 34 of the network side converters 32 to generate voltage pulses that are further transformed by the individual turbine transformers 22 and, optionally, can also be filtered by inductance coils and capacitors, to give voltage signal that meets the frequency requirements and of

15 PCC voltage 16. The voltage signals of different wind turbine electrical systems 18 below are coupled in parallel with the PCC 16. Therefore, a combined sine wave in the PCC is a sum of the voltage signals of all the wind turbine electrical systems 18 and has reduced harmonics.

In a second embodiment of the invention, referring again to Figures 1 and 2, the PWM patterns for a corresponding phase, for example, Ua, of the network side converter 32 in different wind turbine electrical systems 20 are they are offset by a different technique in which the carrier signals for the corresponding phase of different wind turbine electrical systems 18 are the same, and the fundamental waveforms for the corresponding phase of different wind turbine electrical systems 18 are interleaved when displaced one with another evenly throughout a fundamental waveform cycle a degree of 60 / n, in which n is the number of wind turbine electrical systems 18 in the power generation system

25 10. The outdated PWM patterns actuate the switches 34 and generate a plurality of voltage pulses. The turbine transformers 22 can be used to transform the voltage pulses and restore the displaced phases between the wind turbine electrical systems 18.

In a specific embodiment, the PLL circuits 40 of each wind turbine electrical system 18 are electrically coupled with the PCC 16 to obtain a global reference (ie, the same carrier signal and the same fundamental waveform). The fundamental waveforms below are shifted between the wind turbine electrical systems 18. Figure 7 shows such an embodiment in which the carrier signals 162, 262, 362 and 462 and the fundamental waveforms 160, 260, 360 and 460 for a phase, for example, phase Ua, of four wind turbine electrical systems 18 are generated from the global reference. The carrier signals 162, 262, 362 and 462 are the same. The fundamental waveforms 160, 260, 360 and 460 are

35 displaced along the fundamental waveform cycle 15 degrees between adjacent wind turbine electrical systems 18.

Referring to Figure 8, PWM patterns 164, 264, 364 and 464 for a phase of each of the four wind turbine electrical systems 18 are obtained by comparing the fundamental waveforms 160, 260, 360 and 460 with carrier signals 162, 262, 362 and 462. Each of the 40 PWM patterns 164, 264, 364 and 464 is a series of pulses with a common symmetry and amplitude and with slightly different widths of individual pulses. Pulse patterns are shifted along the fundamental waveform cycle 15 degrees. In the exemplary embodiment, the fundamental waveforms 260, 360 and 460 of the second, third and fourth wind turbine electrical systems 18 are displaced respectively 15 degrees, 30 degrees and 45 degrees throughout the shape cycle fundamental waveform with respect to the first waveform

45 fundamental 160 of the first wind turbine electrical system 18.

The outdated PWM patterns actuate the switches 34 of the network side converters 32 and generate a plurality of voltage pulses, and, in one embodiment, each turbine transformer 22 transforms the voltage pulses and resets the PWM offset. In one embodiment that corresponds to the PWM offset shown in Figure 8, the turbine transformer 22 of the first wind turbine electrical system 18 is, for example, a star-star transformer and the waveform is not is displaced The turbine transformers 22 of the second, third and fourth wind turbine electrical systems 18 respectively have a lag of -15, -30 and -45 degrees with respect to the first waveform along the PWM pattern cycle . The turbine transformers 22 of the second, third and fourth wind turbine electrical systems 18 are offset transformers, for example, zigzag transformers or transformers configured in enlarged triangle 55, to restore the angle displaced in the fundamental waveforms . The displaced degrees of the waveforms of the turbine transformers 22 are correlated with the degrees displaced by PWM, that is, the degrees of fundamental waveform displacement. After the PWM offset and reset, only the harmonics of order numbers N · 6 · t ± 1 remain without cancellation, in which t = 1, 2, 3 ..., and N is the number of side converters network 32, that is, the number of wind turbine electrical systems 18

60 in the power generation system 10.

image5

In an alternative embodiment, as discussed above with respect to Figure 2, the PLL circuits 40 of each wind turbine electrical system 18 are electrically coupled with the lower voltage side 21 of each turbine electrical system wind 18 to get a corresponding local reference. The carrier signals and fundamental waveforms of a different wind turbine electrical system 18

5 may have slightly different phases in such local reference embodiments.

As shown in Figure 9, carrier signals 172, 272, 372, 472 and fundamental waveforms 170, 270, 370 and 470 are generated based on local references of different wind turbine electrical systems 18. The Fundamental waveforms 170, 270, 370 and 470 are displaced along the fundamental waveform cycle 15 degrees between adjacent wind turbine electrical systems 18.

In certain embodiments, the PWM patterns for the three phases Ua, Ub and Uc of the network side converters 32 in the same wind turbine electrical system 18 are the same. In one embodiment, if a frequency relationship between the carrier signal and the fundamental waveform is equal to 3 * N, in which N is an integer, the fundamental waveforms for the three phases are offset 120 degrees one with with respect to another throughout the fundamental waveform cycle and are compared with the same carrier signal in such a way that the

15 resulting PWM patterns for all three phases are the same. Harmonic voltages at carrier frequencies are common mode waveforms, therefore they do not contribute to any differential output current. Therefore, harmonics with frequencies of 3 * N times of the fundamental waveform are canceled and not shown in the PCC 16.

In another embodiment, if the frequency relationship between the carrier signal and the fundamental waveform is not equal to 20 to 3 * N, in order to obtain the same PWM pattern for all three phases in the same turbine electrical system image6

wind 18, the three-phase carrier signals are shifted throughout the fundamental cycle one with

Regarding another. The shifted carrier signal is compared with the fundamental waveforms of the three phases that are offset along the fundamental waveform cycle to achieve the same PWM patterns for all three phases.

In another embodiment, the PWM patterns of different wind turbine electrical systems 18 are both interleaved and outdated, and the turbine transformers restore displaced phases in the output waveforms. Up to a certain point, the third embodiment is a combination of the embodiments described above with respect to Figures 5-6 and 7-9 and, hence, a description is hereinafter omitted Similary. As described above with reference to Figure 8,

30 by means of PWM displacement and the restoration by means of a transformer between the four wind turbine electrical systems 18, only the harmonics of orders N · 6 · t ± 1 continue to exist, which can be further reduced by interleaving carrier signals.

In a specific embodiment, the carrier signal between the wind turbine electrical systems 18 is interleaved t * 60 / N degrees, in which N is the number of wind turbine electrical systems 18 in the generation system

35 of power 10 and t is an integer. For the power generation system 10 by way of example in Figure 1 with four wind turbine electrical systems 18, the carrier signals between the wind turbine electrical systems 18 can be interleaved 15 * t degrees.

In a power generation system 10 with at least two electric wind turbine systems 18, each of the image7

order harmonic k of the at least two wind turbine electrical systems 18 is a harmonic vector _k

40 which includes an amplitude component and a Phi_k phase angle component. In one embodiment, a clean harmonic cancellation of a particular order k can be obtained by making a sum of the harmonic vectors of the at least two wind turbine electrical systems 18 void. In one embodiment, the amplitude components of the order harmonic k of the at least two wind turbine electrical systems 18 are substantially the same.

In certain embodiments, the fundamental waveform is expressed as:

Qm cos (kmωt + Phi_m),

in which Qm is an amplitude of the fundamental waveform; Phi_m is a phase angle of the fundamental waveform; km is an order of frequency of the fundamental waveform (and a default value for km is 1), and ω = 2 * π * 60. The triangular carrier waveform is expressed as:

fifty

image8 cos (kmωt + Phi_c),

in which

image9 it is an amplitude of the triangular carrier waveform; Phi_c is a phase angle of the triangular carrier waveform along the triangular carrier waveform cycle; kc is the order of

image10

frequency of the triangular carrier waveform; and ω = 2 * π * 60. For the harmonic of order k, k submits to equation 1:

k = m · kc + n · km. Equation 1

in which m and n are integers respectively.

In one embodiment, the phase angle of the harmonic of order k of the at least two electric wind turbine systems 18 can be expressed, for simplicity, as a matrix in the following equation 2:

image11

-Equation 2

in which Phi_k_1, Phi_k_2, Phi_k_N are respectively phase angles of the harmonic of order k from the first 10, the second and the number N wind turbine electrical systems 18 in the power generation system

10. The first two terms in the right member of the equation are determined by modulating the interleaving of PWM carriers, the third term is triggered by a fundamental PWM waveform shift, and the fourth term is contributed by a phase reset via transformer. Seq (k) is the phase sequence of the harmonic of order k with respect to the fundamental waveform in the PCC.

15 For each of the wind turbine electrical systems 18, the three phases Ua, Ub and Uc of the fundamental waveform in PCC 16 are therefore:

Ua = U · sen ωt

Ub = U · sen (ωt -120º)

Uc = U · sen (ωt + 120º)

20 For the harmonic of order k, the three-phase harmonic voltages are respectively:

Uka = Uk · sen kωt

Ukb = Uk · sen (kωt -k120º)

Ukc = Uk · sen (kωt + k120º)

Seq (k) = 1 represents that the harmonic of order k has a positive sequence with respect to the waveform

25 fundamental; Seq (k) = -1 represents that the harmonic of order k has a negative sequence with respect to the fundamental waveform; and Seq (k) = 0 represents that the harmonic of order k has a null sequence. Harmonics with a null sequence will not be shown in PCC 16. In the exemplary power generation system 10 with four wind turbine electrical systems 18, equation 2 is as follows:

image12

30 The matrix of harmonic phase angles at k = m · kc + n · km is simplified as equation 3 hereafter:

image13

For the harmonic of order k, the second, third and fourth terms of equation 3 are determined, and only the first term that concerns the interleaved phase angle of the carrier signals can be adjusted. In one embodiment, the carrier phase angles throughout the carrier signal cycle of the four converters

35 to be adjusted are in the form of equation 4 hereinafter: in which "kc_adj" is a coefficient of the carrier phase angle adjustment between the wind turbine electrical systems 18.

image14

In one embodiment, the electrical system is in power balancing conditions in which the wind turbine electrical systems 18 have substantially the same DC voltage at the DC busbars 31 and have the same voltage outputs at the PCC 16, and use the same carrier signal for the three phases Ua, Ub and Uc in each wind turbine electrical system 18. In the present embodiment, k = m · kc + n · km, and Seq (k) is determined only by n. Therefore, according to equations 3 and 4, equation 3 can be simplified in equation 5 hereinafter.

image15

Therefore, in an embodiment with references to Figures 10 and 11, a total harmonic in the order k is canceled. image16 image17 image18 image19

when a sum of the harmonic vectors _k_1, _k_2, _k_3, and _k_4 of the first, second, third and fourth wind turbine electrical systems 18 is zero. In one embodiment, because the components of image20 image21 image22 image23

amplitude of the harmonics _k_1, _k_2, _k_3, and _k_4 are substantially the same, by selecting 15 an appropriate Kc_adj coefficient to adjust the phase components of the harmonic vectors according to equations 1 and 5, the sum of vectors Harmonics can be driven to zero.

In one example, to cancel the 25-th harmonics of the power generation system 10 (k = 25) when a frequency of the fundamental waveform is 60 Hz and for a carrier signal frequency it is 780 Hz (kc = 13 ), the equation 1 k = m · kc + n · km is obtained as 25 = 13 m + n. So, a group of values for "m" and

20 "n" is: m = 2, n = -1. Therefore "sequence (n)" in equation 5 is sequence (-1) = -1. Therefore, equation 5 is obtained as:

image24

Therefore, in one embodiment, when kc_adj = 3, Phi_k_1, Phi_k_2, Phi_k_3, and Phi_k_4 are respectively 0 degrees, 450 degrees, 900 degrees, and 1350 degrees, which constitutes the vector diagram of Figure 9, and the 25

25th harmonics are canceled.

In another embodiment, referring to Figure 12, a vector diagram is shown for the cancellation of a harmonic of order k for a power generation system 10 that has five wind turbine electrical systems 18. This can be obtained by selecting an appropriate carrier phase angle coefficient to obtain a zero vector sum of the five wind turbine electrical systems 18.

30 Referring again to Figure 1, in certain embodiments, the power generation system 10 comprises a medium voltage pickup system 80 which is a multi-door network that includes a plurality of inputs that electrically couple the electrical systems of wind turbine 18 and a single output that is electrically coupled to PCC 16. Each wind turbine electrical system 18 is electrically connected to the medium voltage pick-up system (MVCS) 80 by, for example, power cables of

35 medium voltage. An impedance matrix between each wind turbine electrical system 18 and the PCC 16 caused by the MVCS 80 comprises resistance elements, capacitive elements and / or inductive elements, each of which is substantially frequency dependent. The impedance matrix results in a lag both in the fundamental frequency and in the harmonic of order k between voltage signals on the high voltage side 23 of the turbine transformer 22 and in the PCC 16. Reference can be made respectively to the angles displaced

40 totals θl and θk caused by the matrix of impedances at the fundamental frequency and the harmonic of order k as in equations 6 and 7 hereafter:

image25

in which, Phi_pcc is the phase angle of the voltage signal at the fundamental frequency at PCC 16, and Phi_m_N is the phase angle of the voltage signal at the fundamental frequency on the high voltage side 23 of the

5 turbine transformer 22. Phi_kpcc_N is the phase angle of the voltage signal at the harmonic frequency of order k in PCC 16, and Phi_k_N is the phase angle of the voltage signal at the harmonic frequency of order k on the high voltage side 23 of the turbine transformer 22.

According to equations 3, 6, and 7, in order to achieve a null vector sum of the harmonic of order k in the PCC 16, the phase angle matrix of the harmonics in k = m · kc + n · km for the four turbine systems

By way of example, wind power 18 includes the displaced angles caused by the impedance matrix of the MVCS 80. The phase angle matrix in the PCC 16 is then expressed as:

image26

And it can be further simplified as:

image27

15 Consequently, an array of correction factors for the interleaved angles Phi_ccor_N of the carrier signals is shown as equation 8 as hereinafter:

image28

The displaced angles θ1 and θk for each wind turbine electrical system 18 depend on the impedance matrix of the MVCS 80 at the fundamental frequency and the harmonic frequency of order k. In certain 20 embodiments, the power generation system 10 further comprises an impedance measuring device for measuring the impedance matrix of the MVCS 80 in a frequency range, which includes the

image29

fundamental frequency and harmonic frequencies, by any known procedure. In an exemplary embodiment, the impedance matrix of the MVCS 80 can be measured by transmitting a voltage scanned in a plurality of frequency ranges and recording the response impedances at the frequency ranges.

5 In certain embodiments, the resistance elements, the capacitive elements and / or the inductive elements of the impedance matrix of the MVCS 80 can be changed over time, and the turbine controllers 24 and / or the master controller 25 may comprise a system closed loop control. The closed loop control system is connected to an impedance measuring device, and the control of the interleaved angles of the carrier signals of each wind turbine system 18 is based on the matrix of

10 measured impedances of the MVCS 80.

In one embodiment, with reference to Figure 1, the power conversion system 20 of each wind turbine electrical system 18 may include a plurality of wires (not shown), each comprising a generator side converter, a DC busbar, and a network side converter. The wires within a power conversion system 20 are connected in parallel and connected to the turbine transformer 22. In a

15 embodiment, the carrier signals and the fundamental waveforms for each network side converter within a wind turbine electrical system 18 are the same.

In one embodiment, the wind farm 11 comprises a plurality of wind turbine groups, and each group comprises at least two wind turbines that respectively have net side converters. The at least two wind turbines may or may not be physically close to each other and may or may not have a similar assigned power. In a specific embodiment, the at least two wind turbines within a group are controlled by individual turbine controllers or, optionally, by a group controller to interleave carrier signals, fundamental waveforms, or a combination of carrier signals and shapes. fundamental wavelengths of the at least two wind turbines in the group to generate interleaved PWM patterns respectively for the network side converters of the at least two

25 wind turbines. Therefore, the output of each group meets the harmonic requirement in PCC 16.

In another specific embodiment, at least two wind turbines within a group are controlled by the individual turbine controllers or, optionally, by the master controller or a group controller to have a lag in the fundamental waveforms of a degree of 60 / N, in which N is the number of wind turbines in the group, and use a zigzag turbine transformer to restore the displaced angles.

30 Wind turbines in different groups have intercalated carrier signals. While in yet another specific embodiment, at least two wind turbines within a group have intercalated carrier signals. Wind turbines in different groups have an offset in the fundamental waveform of a 60 / M degree, in which M is the number of groups in the wind farm 11, and use the zigzag turbine transformers 22 to restore the displaced angles

35 Referring to FIG. 13, in one embodiment, the wind farm 11 comprises at least one substation system 100 that is connected to the power grid 14 in the PCC 16. The substation system 100 comprises a substation 101 and feeder systems 108 and 110 which are electrically coupled with a common busbar 103 of the substation 101 at electrical connection points such as substation management points (SMP) 102 and 104. In one embodiment, the substation 101 comprises a transformer

40 elevator 112 to transform the medium voltage into a high voltage. In certain embodiments, the wind farm 10 may comprise more substation systems that are connected in parallel in the PCC 16, and each substation system may comprise at least one feeder system.

In one embodiment, each of the feeder systems 108 and 110 comprises a plurality of wind turbine electrical systems 18 that are, for example, connected in daisy-type chain, forked, or dendritically connected -radial with the substation 101 through one or more MVCS multi-door

80. In one embodiment, a control system for controlling the wind turbine electrical systems 18 that are connected through the same MVCS 80 is interleaved, and / or offset (reset by transformer) so that the network side converters achieve harmonic reduction at an electrical connection point that is an output of the MVCS 80, with reference to the harmonic reduction control for PCC 16 in the foregoing. He

The electrical connection point can be any point between the output of the MVCS 80 and the common busbar 103 of the substation 101, for example, points 102, 114 of the feeder system 108.

In certain embodiments, each feeder system 108, 110 may comprise a plurality of groups that are connected by the same MVCS 80, for example, groups 120 and 122, both connected to the same MVCS 80 through the electrical connection points 116 and 118.

Each group 120, 122 comprises at least two electrical wind turbine systems 18 that may or may not be physically close to each other and may or may not have a similar assigned power. In a specific embodiment, at least two wind turbine electrical systems within a group are controlled by individual turbine controllers or, optionally, by a group controller to interleave carrier signals, fundamental waveforms, or a combination of carrier signals. and fundamental waveforms of those by wind turbine electrical systems 18 in a group to generate interleaved PWM patterns respectively for the network side converters of wind turbine electrical systems. Therefore, the output of each group meets the harmonic requirements at electrical connection points 116 and 118.

image30

In another specific embodiment, at least two wind turbines within a group are controlled by the

5 individual turbine controllers or, optionally, by the master controller or a group controller to have an offset in the fundamental waveforms of a 60 / N degree, in which N is the number of wind turbines in the group, and use a zigzag turbine transformer to restore displaced angles. Wind turbines in different groups have intercalated carrier signals. While in yet another specific embodiment, the at least two wind turbines within a group have carrier signals

10 interspersed. Wind turbines in different groups have an offset in the fundamental waveform of a 60 / M degree, in which M is the number of groups in the wind farm 11, and use the zigzag turbine transformers 22 to restore the displaced angles

In certain embodiments, a wind farm electrical system includes a global time reference for each wind turbine electrical system 18. In one embodiment, the global time reference is provided with

15 according to the precision time protocol (PTP) or an IEEE -1588 protocol. In certain embodiments, the PTP or IEEE-1588 protocol is distributed to the individual turbine controllers 24 via communication links, which can be implemented in physical media, software, or combinations thereof.

Although wind turbine systems have been analyzed in the foregoing for example purposes, other forms of renewable energy, such as photovoltaic systems, can be used additionally or as an alternative. In

In one embodiment, a photovoltaic system comprises a plurality of photovoltaic electrical systems that are connected in parallel to supply electrical power to the power grid 14 in the PCC 16.

Referring to Figure 14, which is a block diagram of an exemplary photovoltaic electrical system 82 according to an embodiment disclosed herein, each photovoltaic electrical system 82 includes a DC busbar 86 that receives a current continuous from a photovoltaic module 84, a

25 network side converter 88 comprising a plurality of switches 94 for transmitting DC current on the DC busbar 86 to give alternating currents, and a transformer 90 for transforming the alternating current into a constant voltage and a certain frequency before The alternating current is supplied to the mains 14 in the PCC 16.

Each photovoltaic electrical system 82 includes a PWM 92 modulator to obtain a waveform

30 fundamental and a carrier signal, using the fundamental waveform and the carrier signal to generate a PWM pattern, and to provide the PWM pattern to a respective network side converter to operate the switches 94 of the network side converter 90 respective. The PWM 92 modulators of a different photovoltaic electrical system 82 are configured to interleave carrier signals, fundamental waveforms, or a combination of carrier signals and fundamental waveforms of the at least two electrical systems of

35 wind turbine to generate interleaved PWM patterns respectively for network side converters 90 between different photovoltaic electrical systems 82 to reduce harmonics in PCC 16.

It is to be understood that not necessarily all such objects or advantages as described above can be achieved in accordance with any particular embodiment. Therefore, for example, those skilled in the art will recognize that the systems and techniques described herein can be performed.

40 or be carried out in a manner that achieves or optimizes an advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

In addition, the expert will recognize the interchangeability of various characteristics from different embodiments. The various features described, as well as other known equivalents for each feature,

45 may be mixed and corresponded by an expert in the present field to build additional systems and techniques in accordance with principles of the present disclosure.

Although only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. Therefore, it should be understood that the appended claims are intended to cover all such modifications and changes

50 as they fall within its scope.

Claims (6)

image 1 1. A power generation system (10) comprising: at least two electrical systems (18) connected by means of a medium voltage collection system (80) with an electrical connection point (16), said electrical connection point (16) being a common connection point with 5 a network (14), each electrical system (18) comprising a power conversion system (20) comprising a respective DC to AC converter (32) that includes a plurality of switches (34) to convert a power into current continuous in a power in alternating current; Y a control system (24, 25) that includes at least two pulse width modulation modulators (36), each pulse width modulator (36) obtaining a fundamental waveform to generate a pattern of 10 pulse width and to provide the pulse width pattern to a respective DC to AC converter (32) to operate the switches of the respective DC to AC converter (32); wherein the control system (24, 25) is configured to interleave the fundamental waveforms of the at least two electrical systems to generate interleaved pulse width patterns respectively for the at least two DC to AC converters (32 ), 15 in which each power conversion system (20) further comprises a generator side converter (30) respective to convert a power into alternating current from a wind turbine generator (28) into a power in direct current; Y wherein the control system further comprises a master controller (25) connected to the electrical connection point (16), characterized in that: 20 the pulse width modulators (36) additionally obtain a carrier signal and use the fundamental waveform and the carrier signal to generate a pulse width pattern, and the control system (24, 25) is further configured to interleave the fundamental waveforms and carrier signals or a combination of the fundamental waveforms and carrier signals. 2. The power generation system (10) of claim 1, wherein the electrical connection point (16) is a connection point of said at least two electrical systems (18) coupled in parallel.

3.

The power generation system (10) of any preceding claim, wherein the control system (24, 25) includes at least two turbine controllers (24) respectively for electrical systems (18).

Four.

The power generation system (10) of any preceding claim, wherein the carrier signal comprises a triangular waveform.

The power generation system (10) of any preceding claim, wherein each pulse width modulator (36) is configured to receive a reference signal from the electrical connection point (16) to generate the carrier signal and the fundamental waveform. 6. The power generation system (10) of any preceding claim, wherein each modulator by Pulse width (36) is configured to receive a reference signal from the respective network side converter 35 (32) to generate the carrier signal and the fundamental waveform. 7. The power generation system (10) of any preceding claim, wherein the fundamental waveforms of the at least two electrical systems (18) are displaced along a fundamental waveform cycle one with respect to to another a degree of 60 / n, and n is the number of electrical systems of the power generation system (10). The power generation system (10) of any preceding claim, wherein each converter on the network side (32) is configured to receive direct current from a photovoltaic module (84). 12